Abstract

The absorptionspectrum of jet-cooled 2,3-benzofluorene (Bzf) has been measured by cavity ring-down spectroscopy. The potential energy surfaces of the states of Bzf have been investigated with calculations based on the time-dependent density functional theory (TD-DFT). At the B3LYP/TZ level of theory, TD-DFT does not deliver a realistic difference between the excited and potential energy surfaces, a problem which can be avoided by introducing a reference geometry where this difference coincides with the observation. In this geometry, an expression for the Herzberg–Teller corrected intensities of the vibronic bands is proposed, allowing a straightforward assignment of the observed modes below , including realistic calculated intensities. For vibronic bands at higher energies, the agreement between calculated and observed modes is deteriorated by substantial Dushinsky rotations and nonparabolicities of the potential energy surface.

Received 23 May 2008Accepted 11 July 2008Published online 18 August 2008

Acknowledgments:

This work was supported by a cooperation between the Max Planck Institute for Astronomy and the Friedrich-Schiller-Universität Jena as well as by the Deutsche Forschungsgemeinschaft (DFG) in the framework of the Forschergruppe Laborastrophysik. The authors are grateful to K. P. Geigle for fruitful discussions and for communicating calculated semiempirical intensities as well as to M. Vala for providing his computational results regarding the vibrational energies of Bzf in its electronic ground state. We wish to thank M. Schreiber for giving us the opportunity to use the computational facilities at Technische Universität Chemnitz.